The incidental finding of malignant internal thoracic lymph nodes while mobilizing the internal thoracic artery (ITA) for coronary bypass grafting has not to our knowledge been previously reported. The cases of 3 male patients who underwent surgery between January 1990 and January 1993 and in whom malignant lymph nodes were found in the ITA pedicle are reviewed. One individual was found to have metastatic carcinoma of the breast, whereas the other 2 were discovered to have previously undiagnosed lymphomas. After undergoing further relevant investigation and treatment, all 3 patients remain free of recurrent disease 6.8 to 9.8 years after their original cardiac surgery. Primary or metastatic malignancy may be encountered in the course of ITA mobilization for grafting. Abnormally enlarged internal thoracic lymph nodes should be sent for pathologic examination.